This invention relates to a stepless speed change device for general purpose suitable for use in industrial machines, transportation facilities and the like.
In general, a speed change device enabling speeds to change stepwise has disadvantages in that shocks occur when the speeds are stepwise changed and optimum speeds are difficult to obtain because intermediate speeds could not be set other than the stepwise determined speeds.
A stepless speed change device eliminates such disadvantages of the speed change device. Mechanical stepless speed change devices have been practically used which are mostly friction wheel type stepless speed change devices. One example is that disclosed in Japanese Utility Model Application Publication No. 49-29,168.
With such a hitherto used friction wheel type device, the stepless speed change is accomplished by stepless changing rotating radii at contacting points of conical wheels for friction transmission. However, the contacting surfaces of the conical wheels are wide belt-like surfaces along contacting orbits corresponding to pitch lines due to Hertz stresses. As a result, positive and negative slips occur on larger and smaller diameter sides of the contacting orbit so that such slips result into internal friction losses to lower the transmission efficiency.
Moreover, when the transmission ratio is maximum or minimum, the positive and negative slips above described are rapidly increased because a ratio of pitch line diameters of the driving and driven friction wheels at friction transmission contacting points is fairly large such as from 1:2 to 1:4. Therefore, the transmission efficiency is considerably decreased in fastest and lowest speed ranges.